Pneumatic tire with circumferential and transversal reinforcement layers

ABSTRACT

A pneumatic tire to effectively enhance the transversal stiffness and prevented the carcass from breaking before the other reinforcement members break is provided. A tread rubber is arranged radially outwardly on the crown portion of the carcass. A belt consisting of at least one belt layer is arranged between the tread rubber and the carcass. The belt layer containing cords extending in a direction inclined from the tire&#39;s circumferential direction. At least one circumferential reinforcement layer containing meandering cords extending generally along the tire&#39;s circumferential direction in a wavy or zigzag shape is provided radially outwardly or inwardly on the belt or between the belt layers. At least one transversal reinforcement layer containing straight cords extending generally perpendicular to the tire&#39;s circumferential direction is provided on the position radially outwardly adjacent to the crown portion of the carcass.

TECHNICAL FIELD

The present invention relates to a pneumatic tire for heavy load havinga tread portion whose transversal strength has been enhanced, and morespecifically a pneumatic tire suitable for use in a truck or a bus.

BACKGROUND ART

A pneumatic tire for heavy load generally has a belt radially outwardlyarranged on a carcass to reinforce a tread portion. The belt used isusually a crossing belt having multiple layers of which cordsalternatively crossed with each other between the layers, or an inclinedbelt having a single belt layer of which cords are inclined to thetire's circumferential direction.

When such a tire is subjected to inflation pressure, a hoop effect ofthe belt becomes smaller at a tread shoulder portion than at a treadcenter portion and thus the amount of a radial growth of the belt at thetread shoulder portion becomes larger than that at the tread centerportion. Consequently, the tread shoulder portion of the beltextensionally deforms relatively large in the circumferential direction,which causes a large circumferential strain on the tread rubber. As aresult, there is a problem that a separation is apt to occur between thebelt and the tread rubber.

Further, pneumatic tires for heavy load recently tend to have lowerprofiles in response to increasing demands for lowering a vehicle floorand making a drive shaft or a trailer shaft to be single wheeled insteadof traditional dual wheeled. When such a low-profile tire, especially atire having an aspect ratio of 70% or less is subjected to inflationpressure, the amount of the radial growth tends to further increase atthe shoulder portion.

JP 2-208101A describes that a reinforcement layer containing meanderingcords extending along the circumference direction in a wavy or zigzagshape is provided radially outwardly or inwardly on the belt or betweenthe belt layers as a means for suppressing the radial growth of the beltat the tread shoulder portion, and it has been used up to now. This cansuppress the radial growth of the belt at the tread shoulder portion,thereby improving the durability of the tread shoulder portion.

For the tires having such a configuration, it has been considered thatthe transversal stiffness is not necessarily reinforced during the innerpressure being applied, since a load of the circumferential tensileforce is large while a load of the transversal tensile force is smallduring the inner pressure being applied. However, if an input such as aprojection is penetrated, the tire is easily bent and pulled in thetransversal direction due to its small transversal tensile stiffness, sothat carcass cords, which are transversal members, are subjected tolarger input forces. For example, when the tire receives a projectioninput caused by passing over a stone during running on the road, thetire tends to deform more in the transversal direction than in thecircumferential direction as compared with the ordinal tire.

The term “projection input” herein refers to a radially inward forceacting on the tread surface when a pneumatic tire runs on the road andpasses over, for example, a stone.

When the tire having such a tendency runs while repeatedly incurring theprojection input, the carcass which mainly contributes the transversalstiffness breaks prior to the belt which mainly contributes thecircumferential stiffness. A problem is that the tire gets blowoutand/or tread burst much easier in the case where the carcass breaksfirst than in the case where the belt breaks first.

Further, a demand for improving transport efficiency in the modernmarket needs enhancements of speed and load capacity of the vehicle.From this viewpoint also, the durability of the carcass may becomeproblematic.

In this connection, it is recently noticed that, in order to improve thedurability of the carcass against the projection input, the transversalstiffness of the tread portion may be enhanced to suppress thetransversal deformation occurring at the time of receiving theprojection input, thereby decreasing the input force per one cord in thecarcass.

JP 2002-514538A, for example, describes a tire in which an additionalply having substantially radially arranged reinforcement elements ofnon-extensible metal is provided between belt layers. The tire, however,is provided with the transversal reinforcement layer between the beltlayers, so that the effect of reinforcing the carcass is not sufficient.JP 4-356203A describes a tire comprising belt layers among which theinner most belt layer in the tire's radial direction is dividedlyarranged with spacing the central region to form a split configuration,and a reinforcement layer in which radial cords are embedded, thereinforcement layer being arranged inside these belt layers in thetire's radial direction and along the carcass. The tire, however, has noreinforcement around the tire's equatorial plane at which largestdeformation is observed at the time of receiving the projection input,so its durability is not sufficient. JP 2002-192910A describes a tire inwhich transversal reinforcement layers having cords extending at 50 to90 degrees with respect to the tire's circumferential direction arearranged between a carcass and a belt and between the shoulder portionand the tire's equatorial plane. The object of the tire, however, is notan improvement of the durability, but an improvement of the drivability.In addition, the tire has no reinforcement around the tire's equatorialplane at which largest deformation is observed at the time of receivingthe projection input, so its durability is not sufficient. Furthermore,in the tire for heavy load having such a belt configuration, theabove-mentioned projection input is easily transmitted to the carcassand thus the ply cords are readily broken, which is problematic.

As a measure for enhancing a transversal stiffness of a tread portion,enlarging the diameter of carcass ply cords and increasing the number ofcarcass ply cords embedded in the carcass may be recited by way ofexample. However, these measures involve a demerit of increasing theweight of the whole tire, and a stepwise transition of the stiffnessoccurring at a rolled-up end of the carcass becomes greater, whichinvolves another demerit of decreasing the durability at the rolled-upend of the carcass.

DISCLOSURE OF THE INVENTION

The present invention is directed to solve these problems which theconventional art has. The object of the present invention is to providea pneumatic tire for heavy load which can prevent an increase of theweight of the whole tire although the tire adopts a configuration inwhich a reinforcement layer for enhancing the transversal stiffness isarranged to suppress a radial growth of a belt, as well as caneffectively enhance the transversal strength without involving adecrease of the durability at the carcass ends, so that the carcass canbe prevented from breaking before the other reinforcement members suchas a belt and a reinforcement layer break.

A pneumatic tire according to the present invention comprises a carcasscontaining at least one toroidal carcass ply, a tread rubber arrangedradially outwardly on the crown portion of the carcass, and a beltconsisting of at least one belt layer arranged between the tread rubberand the carcass, the belt layer containing cords extending in adirection inclined from the tire's circumferential direction, wherein atleast one circumferential reinforcement layer containing meanderingcords extending generally along the tire's circumferential direction ina wavy or zigzag shape is provided radially outwardly or inwardly on thebelt or between the belt layers, and at least one transversalreinforcement layer containing straight cords extending generallyperpendicular to the tire's circumferential direction is providedradially outwardly on the position adjacent to the crown portion of thecarcass.

The transversal reinforcement layer is provided radially outwardly onthe position adjacent to the carcass in this tire, so that, when aprojection input penetrates the carcass, the stiffness of the straightcords extending generally perpendicular to the tire's circumferentialdirection in the transversal reinforcement layer bears a transversalforce near the carcass caused by the projection input to suppress abending deformation and more effectively decrease a bending tensiledeformation input acting on the carcass. As a result, the carcass can beprevented from breaking before the other reinforcement members such asthe belt and the reinforcement layer break.

At least one circumferential reinforcement layer containing themeandering cords extending generally along the tire's circumferentialdirection in a wavy or zigzag shape is provided radially inwardly oroutwardly on the belt or between the belt layers, so that the radialgrowth of the belt at the tread shoulder portion can be more effectivelysuppressed to prevent the separation between the belt and the treadrubber.

In addition, the transversal reinforcement layer is provided only on thecrown portion of the carcass which needs to enhance its transversalstrength, so that the increase in weight of the whole tire can besuppressed and the number of carcasses as well as the stepwisetransition of the stiffness at the folding end can be reduced ascompared with a tire having a structure in which a plurality ofcarcasses are used to obtain the similar transversal strength. As aresult, the transversal strength can be more effectively enhanced.

In a preferred embodiment of the invention, the inclined angle of thestraight cords of the transversal reinforcement layer with respect tothe tire's circumferential direction may be within a range of 90±20degrees.

According to this embodiment, the extending direction of the straightcords is set as close to perpendicular as possible with respect to thetire's circumferential direction, so that the transversal stiffness canbe more effectively enhanced and the increase in weight of the tire canbe more effectively suppressed.

On one hand, the optimal inclined angle of the straight cords withrespect to the tire's circumferential direction is 90 degrees withconsidering only the transversal strength. On the other hand, when atensile force occurs in the tire's circumferential direction in themolding process, the cords cannot bear the tensile force and, as aresult, the arrangement of the cords tends to be disordered. The cord ispreferably inclined from 90 degrees in order to prevent the disorder ofthe arrangement, but the transversal stiffness will suddenly drop if theinclined angle deviates from the range of 90±20 degrees. In the light ofthese characteristics, the suitable inclined angle is decided within therange of 90±20 degrees.

In another preferred embodiment of the invention, the sum of thetransversal strengths of the carcass, the transversal reinforcementlayer, the circumferential reinforcement layer and the belt includingtheir coating rubbers may be 30 kN/25 mm or more at the tire'sequatorial plane. According to this embodiment, the input penetratingthe carcass cords which input is caused by the bending tensiledeformation of the carcass due to the repeatedly occurring projectioninput can be reduced by improving the tensile strength of the wholetread portion. As a result, the carcass can be prevented from breakingbefore the other reinforcement members such as a belt and areinforcement layer break.

In yet another preferred embodiment of the present invention, the ratioof the sum of the transversal strengths of the carcass, the transversalreinforcement layer, the circumferential layer and the belt includingtheir coating rubbers to the sum of the circumferential strengths ofthem may be 0.55 or more at the tire's equatorial plane.

According to this embodiment, the bending tensile deformation of thecarcass due to the repeatedly occurring projection input can be reduced,and the deformation of the carcass in the tire's transversal directionand the deformations of the belt and the circumferential reinforcementlayer in the tire's circumference direction can be appropriatelybalanced, so that the carcass can be prevented from breaking before theother reinforcement members such as a belt and a reinforcement layerbreak.

The transversal strength of each layer can be expressed by the followingequation, where θ is the inclined angle of cords contained in each ofthe carcass, the transversal reinforcement layer, the circumferentialreinforcement layer and the belt with respect to the tire'scircumferential direction;[the transversal strength of each layer]=[the strength of eachcord](N)×[the number of cords embedded](the number of cords/25 mm)×(sinθ)²

The transversal strengths are calculated for each of the carcass, thetransversal reinforcement layer, the circumferential reinforcement layerand the belt, and the results are summed to give the transversalstrength of the tire at the equatorial plane.

The circumferential strength of each layer can be similarly expressed bythe following equation;[the circumferential strength of each layer]=[the strength of eachcord](N)×[the number of cords embedded](the number of cords/25 mm)×(cosθ)²

The circumferential strengths are calculated for each of the carcass,the transversal reinforcement layer, the circumferential reinforcementlayer and the belt, and the results are summed to give thecircumferential strength of the tire at the equatorial plane.

In a further preferred embodiment of the invention, the belt may consistof one belt layer, and the inclined angle of the cords of the belt layerwith respect to the tire's circumferential direction may be 10 to 60degrees.

According to this embodiment, the tensile force of the cords of the beltlayer can bear the forces in the tire's transversal and circumferentialdirections. Therefore, a transversal force required for the corneringand a traction force during the acceleration or deceleration can beensured. In addition, the tensile force of the cords of the belt layercan widely scatter an impact and a deformation which are locallygenerated on the tread's grounding face.

As an alternative to the above-mentioned belt, the belt may consist oftwo or more belt layers; the cords of the adjacent belt layers crosseach other; the inclined angle of the cords of the belt layers withrespect to the tire's circumferential direction is 10 to 60 degrees; andthe cords of the radially adjacent belt layers extend in the mutuallyopposite directions with respect to the tire's circumferentialdirection.

According to this embodiment, the tensile force of the cords of the twoor more belt layer can bear the force in the tire's transversal andcircumferential directions more effectively than in the case where thebelt consists of one belt layer. Therefore, a transversal force requiredfor the cornering and a traction force during the acceleration ordeceleration can be further ensured, as well as an impact and adeformation, which are locally generated on the tread's grounding face,can be more widely scattered.

Preferably, the width of the transversal reinforcement layer is 0.35times or more as large as the tread width. According to thisconfiguration, the transversal strength of a region having a width of0.3 times of the tread width with the tire's equatorial plane as itscenter, where the reinforcement layer is likely to be damaged by theprojection input, can be reinforced by the transversal reinforcementlayer.

As used herein, the term “tread width” refers to the maximum groundingwidth measured when the tire is mounted on a standard rim specified in aspecification such as TRA, ETRTO and JATMA, air is applied to give ainner pressure corresponding to the maximum load for single wheel of theapplicable size defined in the specification, and the maximum load forsingle wheel of the applicable size defined in the specification isloaded.

The width of the transversal reinforcement layer is preferably 0.95times or less as large as the tread width. This enlarges the amount of acompressive deformation in the tire's radial direction at the treadends. So the tread rubber is pushed out to deform in the tread's widthdirection, and the tread rubber near the transversal ends of thetransversal reinforcement layer follows the deformation and is pulledoutward in the tread's width direction, which can prevent a separationbetween the transversal ends of the transversal reinforcement layer andthe tread rubber.

The straight cords constituting the transversal reinforcement layer arepreferably non-extensible cords. This enlarges an initial resistanceforce against the projection input, so that the cords of carcass ply canbe effectively prevented from breaking even in the case of theprojection input having a large initial pressing force.

Alternatively, the straight cords constituting the transversalreinforcement layer may be extensible cords having an initial elongationof 0.2% or more. This enables the transversal reinforcement layer tobendingly deform and wrap around the projection, so that the carcass plycan be prevented from breaking.

The reason is discussed here. There is a positive relationship betweenthe strength of the cords of the carcass ply and the plungercharacteristics. The plunger characteristics are quantified as energydefined by the area of the triangle surrounded by the pressingforce-stroke diagram in FIG. 3. Thus, in order to improve the plungercharacteristics, at least one of the maximum pressing force and themaximum stroke until the tire is broken may be enlarged to increase theabove-mentioned area. Accordingly, if the transversal reinforcementlayer is configured by using the extensible cords having an initialelongation of 0.2% or more, the maximum stroke becomes larger and thusthe plunger characteristics can be improved. As a result, the cords of acarcass ply can be effectively prevented from breaking.

If the cords of the carcass ply have to be further prevented from beingdamaged by the projection input, the initial elongation of the straightcord is preferably 0.7% or more. The larger the initial elongation ofthe straight cord is, the greater the maximum stroke becomes, wherebythe plunger characteristics is expected to be improved.

The straight cords constituting the transversal reinforcement layer arepreferably extensible organic fiber cords. This reduces the stepwisetransition of the stiffness at the ends of the straight cord, so thatthe transversal reinforcement layer easily follows a deformation at thetime of applying a heavy load and a separation from the ends is unlikelyto occur.

Alternatively, instead of using organic fiber cords, the straight cordsconstituting the transversal reinforcement layer may be extensible steelcords. This particularly enhances the bending stiffness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half sectional view of a tread portion in the transversaldirection, showing a tire according to one embodiment of the invention;

FIG. 2 is a development of the tire shown in FIG. 1, showing itsreinforcement structure of the tread portion; and

FIG. 3 is a pressing force-stroke diagram showing plungercharacteristics.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, illustrative embodiments of the invention will be describedwith reference to the attached drawings.

FIG. 1 is a half sectional view of a tread portion in the transversaldirection, showing a tire according to one embodiment of the invention.In this figure, the reference numeral 1 denotes a carcass, and thereference numeral 2 denotes a tread rubber arranged radially outwardlyon the crown portion of the carcass.

In this case, a belt 5 consisting of two belt layers 3, 4 is arrangedbetween the tread rubber 2 and the carcass 1 which toroidally extendsbetween not-shown bead cores. There are also provided twocircumferential reinforcement layers 6, 7 radially inwardly adjacent tothe belt 5 and a transversal reinforcement layer 8 radially outwardlyadjacent to the carcass 1.

FIG. 2 is a development of the tire shown in FIG. 1, showing itsreinforcement structure of the tread portion.

A plurality of straight cords 9 extending generally perpendicular to thetire's circumferential direction are embedded in the transversalreinforcement layer 8 and are coated with coating rubber.

The inclined angle of the straight cords 9 with respect to the tire'scircumferential direction is within a range of 90±20 degrees. One of thereasons of this is that the optimum inclined angle is 90 degrees withconsidering only the transversal strength. On the other hand, when atensile force occurs in the tire's circumferential direction during themolding process, the cords cannot bear the tensile force and, as aresult, the arrangement of the cords tends to be disordered. The cord ispreferably inclined from 90 degrees in order to prevent the disorder ofthe arrangement, but the transversal stiffness will suddenly drop if theinclined angle deviates from the range of 90±20 degrees. In the light ofthese characteristics, the suitable inclined angle is decided within therange of 90±20 degrees.

When the projection input penetrates, the strength of the straight cords9 of the transversal reinforcement layer 8 bears the force near thecarcass due to the projection input to be able to more effectivelyreduce the bending deformation input to the carcass 1. Thus, the carcass1 can be prevented from breaking before the other reinforcement memberssuch as a belt and a reinforcement layer break.

In addition, the transversal reinforcement layer 8 is provided only onthe crown portion of the carcass where the transversal strength has tobe enhanced, so the increase in weight of the whole tire is minimized ascompared with the case where the cords of the carcass ply themselves aremade larger in their diameter or the case where the number of the cordsembedded in the carcass ply is increased. As the result, the transversalstrength can be effectively enhanced without causing a deterioration ofthe durability due to the increase of the stepwise transition of thestiffness at the rolled-up end, and thereby more effectively enhancingthe transversal strength.

The circumferential reinforcement layers 6, 7 contain a plurality ofnon-extensible meandering cords made of, for example, steel or aramidfiber. The cords extend in a wavy or zigzag shape, such as a triangularwave, a square wave or a sinusoidal wave, with respect to the tire'scircumferential direction at the same amplitude and cycle and atdifferent phases. Also, the cords are coated with coating rubber.

With these layers, the amount of a radial growth at the shoulder portionof a low-profile tire can be suppressed under the condition of beingpressurized by air. Further, as the meandering cords extend in a wavy orzigzag shape, a radial expansion during the manufacturing process can beensured.

Moreover, by stacking the circumferential reinforcement layers 6, 7, thelayers containing the meandering cords 10 extending generally along thetire's circumferential direction in a wavy or zigzag shape areoverlapped with each other, so that, when viewed from the outward in thetire's circumferential direction, the arranged meandering cords 10 havedifferent phases with respect to the circumferential direction betweenthe layers and overlap with each other to form a mesh.

In the belt layer 3, a plurality of belt layer cords 11 leaning to theleft with respect to the tire's circumferential direction are arrangedand they are coated with the coating rubber. In the belt layer 4, aplurality of belt layer cords 11 are arranged to be leaned to the rightat the same angle with respect to the tire's circumferential directionas that of the belt layer cords 11 in the belt layer 3 with respect tothe tire's circumferential direction, and they are coated with thecoating rubber.

In this case, the sum of the transversal strengths of the carcass 1, thetransversal reinforcement layer 8, the circumferential reinforcementlayers 6, 7 and the belt layers 3, 4 including their coating rubbers are34 kN/25 mm at the tire's equatorial plane, which is greater than 30kN/25 mm.

The ratio of the sum of the transversal strengths of the carcass 1, thetransversal reinforcement layer 8, the circumferential reinforcementlayers 6, 7 and the belt layers 3, 4 including their coating rubbers tothe sum of the circumferential strengths of them are 0.9 at the tire'sequatorial plane, which is greater than 0.55.

More preferably, the inclined angles of each of belt layer cords 11 withrespect to the tire's circumferential direction are 10 to 40 degrees.

In this case, the belt 5 is formed by two belt layers 3, 4 and theinclined angle of the belt layer cord with respect to the tire'scircumferential direction is 10 to 60 degrees.

Alternatively, instead of using the above-mentioned belt, the belt maybe formed by one belt layer, and the inclined angle of the belt layercords with respect to the tire's circumferential direction may be 10 to60 degrees.

Preferably, a not-shown protective layer in which not-shown protectivelayer cords are arranged at an inclined angle of 40 to 80 degrees withrespect to the circumferential direction and which are coated with thecoating rubber are provided radially outwardly on the belt layer 3, 4.

With this protective layer, the tensile force of the protective layercords can bear the force due to the projection input and thus can reducethe projection input to the belt layer cords 11 of the radiallyoutermost belt layer 3 of the belt 5 to prevent the belt layer cords 11or the meandering cords 10 from breaking. In addition, the inclinedangle of the protective layer cords with respect to the tire'scircumferential direction is equal to or more than the inclined angle ofthe belt layer cords 11 with respect to the tire' circumferentialdirection, so that the amount of the tensile force borne by theprotective layer itself can be reduced and the protective layer can beprevented from breaking.

The circumferential reinforcement layers 6, 7 arranged radially inwardlyon the belt 5 is shown here by way of example, but they may be arrangedradially outwardly or between the belt layers.

More preferably, the width L of the transversal reinforcement layer 8 isset to be 0.35 times or more of the tread width N.

According to this configuration, the transversal strength of a regionhaving a width of 0.3 times of the tread width with the tire'sequatorial plane as its center, where the reinforcement layer is likelyto be damaged by the projection input, can be reinforced by thetransversal reinforcement layer.

More preferably, the width L of the transversal reinforcement layer 8 isset to be 0.95 times or less of the tread width N.

This enlarges the amount of a compressive deformation in the tire'sradial direction at the tread ends. So the tread rubber is pushed out todeform in the tread's width direction, and the tread rubber near thetransversal ends of the transversal reinforcement layer follows thedeformation and is pulled outward in the tread's width direction, whichcan prevent a separation between the transversal ends of the transversalreinforcement layer and the tread rubber.

The straight cords 9 constituting the transversal reinforcement layer 8are preferably non-extensible cords such as made of steel or aramidfiber. This suppresses the amount of a radial growth of a low-profiletire under the condition of being pressurized by air.

Alternatively, instead of using the non-extensible cords, the straightcords 9 constituting the transversal reinforcement layer 8 may beextensible cords having an initial elongation of 0.2% or more. Thisenables the transversal reinforcement layer to bendingly deform and wraparound the projection, so that the carcass ply can be prevented frombreaking

The straight cords 9 constituting the transversal reinforcement layer 8are preferably extensible organic fiber cords such as aramid fiber,polyethylene naphthalate (PEN), and polyethylene terephthalate (PET).This reduces the stepwise transition of the stiffness at the ends of thestraight cord, so that the transversal reinforcement layer easilyfollows a deformation at the time of applying a heavy load and aseparation from the ends is unlikely to occur.

Alternatively, instead of using organic fiber cords, the straight cords9 constituting the transversal reinforcement layer 8 may be extensiblesteel cords. This particularly enhances the bending stiffness.

EXAMPLES Example 1

As an example of the invention, low-profile pneumatic tires for heavyload having tire sizes of 435/45 R22.5 and 285/60 R22.5 are prepared forthe purpose of evaluating their characteristics of preventing precedentbreakings of the carcass when a projection input penetrates a pneumatictire for heavy load which has a transversal reinforcement layer radiallyoutwardly adjacent to the carcass, and a circumferential reinforcementlayer arranged radially outwardly or inwardly on a belt or between beltlayers. The tires are mounted on rims having rim sizes of 14.00×22.5 and9.00×22.5, respectively, and air is applied to them to give the internalpressure of 900 kPa. A hemispheric projection having a diameter of 40 mmis pressed against the tread portion at the tire's equatorial plane.After any one reinforcement layers among the carcass, the belt, thecircumferential reinforcement layer, or the transversal reinforcementlayer breaks, the presence of the precedent breaking of the carcass isexamined and the energy applied until any of the reinforcement layerbreaks (hereinafter referred to as breaking energy) is measured. Thelatter is evaluated by an index calculated with the breaking energy ofthe after-mentioned comparative example 3 as a control. The breakingenergy is obtained by performing integration of the pressing force ofthe above-mentioned hemispheric projection to the amount of pressing atwhich the reinforce layer breaks. The results are shown in Tables 1 to5.

Also, for the purpose of evaluating the effect of the ratio of the widthof the transversal reinforcement layer to the tread width on thesuppression of cracks of the tread rubber at the transversal ends of thetransversal reinforcement layer in the above-mentioned tire, a runningtest on a drum is conducted at the inner pressure of 900 kPa underloading conditions of 63.7 kN (which is the standard load×1.3) for thetire having the tire size of 435/45 R22.5 and 40.2 kN (which is thestandard load×1.3) for the tire having the tire size of 285/60 R22.5,and the presence of cracks of the tread rubber at the transversal endsof the transversal reinforcement layer is measured after running 10,000km. The results are also shown in Tables 1 to 5.

The greater the index of the breaking energy in Tables 1 to 5 is, thehigher the durability for the repeated projection input is.

Depending on the presence of the transversal reinforcement layer, thewidth of the transversal reinforcement layer, the ratio of the width ofthe transversal reinforcement layer to the tread width, the inclinedangle of the straight cords of the transversal reinforcement layer withrespect to the tire's circumferential direction, the number and theposition of the circumferential reinforcement layer, the width of thecircumferential reinforcement layer, the number of belt layer, theinclined angle of the belt layer cords with respect to the tire'scircumferential direction, the presence of the protective layer, theinclined angel of the protective layer cords with respect to the tire'scircumferential direction, the sum of the transversal strength at thetire's equatorial plane, the ratio of the transversal strength to thecircumferential strength, and the presence of the extensibility of thestraight cords, all of which are shown in Tables 1 to 5, sixteenexamples and six comparative examples are prepared and subjected to thetest.

TABLE 1 435/45R22.5 Comparative Example 1 Comparative Example 2Structure Cir. reinf. layer 1(0, 330) Cir. reinf. layer 1(0, 330)(Inclined angle of each cord, Cir. reinf. layer 2(0, 330) Cir. reinf.layer 2(0, 330) width of each layer) Belt layer 1(R20, 210) Belt layer1(R52, 210) Belt layer 2(L20, 190) Belt layer 2(L52, 190) Sum oftransversal strengths at 16.3 17.7 tire's equatorial plane Transversalstrength/ 0.23 0.53 circumferential strength Breaking energy 76 100Presence of preceding break of Yes Yes carcass Trans. reinf. layerwidth/tread width — — Presence of break at ends of trans. — — reinf.layer during drum testing Straight cord constituting trans.Non-expansible steel cord Non-expansible steel cord reinf. layer Example1 Example 2 Structure Trans. reinf. layer (90, 160) Trans. reinf. layer(90, 160) (Inclined angle of each cord, Cir. reinf. layer (0, 330) Cir.reinf. layer (0, 330) width of each layer) Cir. reinf. layer (0, 330)Cir. reinf. layer (0, 330) Belt layer 1(R20, 210) Belt layer 1(R20, 210)Belt layer 2(L20, 190) Belt layer 2(L20, 190) Sum of transversalstrengths at 25.4 30.8 tire's equatorial plane Transversal strength/0.43 0.51 circumferential strength Breaking energy 112 118 Presence ofpreceding break of None None carcass Trans. reinf. layer width/treadwidth 0.42 0.42 Presence of break at ends of trans. None None reinf.layer during drum testing Straight cord constituting trans.Non-expansible steel cord Non-expansible steel cord reinf. layer

TABLE 2 435/45R22.5 Example 3 Example 4 Structure Trans. reinf. layer(90, 160) Trans. reinf. layer (90, 260) (Inclined angle of each cord,width Cir. reinf. layer 1(0, 330) Cir. reinf. layer 1(0, 330) of eachlayer) Cir. reinf. layer 2(0, 330) Cir. reinf. layer2 (0, 330) Beltlayer 1(R52, 210) Belt layer 1(R52, 210) Belt layer 2(L52, 190) Beltlayer 2(L52, 190) Sum of transversal strengths at tire's 31.4 34equatorial plane Transversal strength/circumferential 0.84 0.9 strengthBreaking energy 132 148 Presence of preceding break of carcass None NoneTrans. reinf. layer width/tread width 0.42 0.68 Presence of break atends of trans. None None reinf. layer during drum testing Straight cordconstituting trans. reinf. Non-expansible steel cord Non-expansiblesteel cord layer Example 5 Example 6 Structure Trans. reinf. layer (90,260) Trans. reinf. layer (90, 380) (Inclined angle of each cord, widthCir. reinf. layer 1(0, 330) Cir. reinf. layer 1(0, 330) of each layer)Cir. reinf. layer 2(0, 330) Cir. reinf. layer 2(0, 330) Belt layer1(R52, 210) Belt layer 1(R52, 210) Belt layer 2(L52, 190) Belt layer2(L52, 190) Sum of transversal strengths at tire's 40.1 40.1 equatorialplane Transversal strength/circumferential 1.05 1.05 strength Breakingenergy 159 159 Presence of preceding break of carcass None None Trans.reinf. layer width/tread width 0.68 1.00 Presence of break at ends oftrans. None Yes reinf. layer during drum testing Straight cordconstituting trans. reinf. Non-expansible steel cord Non-expansiblesteel cord layer Example 7 Example 8 Structure Trans. reinf. layer (90,260) Trans. reinf. layer (90, 260) (Inclined angle of each cord, widthCir. reinf. layer 1(0, 330) Cir. reinf. layer 1(0, 330) of each layer)Cir. reinf. layer 2(0, 330) Cir. reinf. layer 2(0, 330) Belt layer1(R52, 210) Belt layer 1(R52, 210) Belt layer 2(L52, 190) Belt layer2(L52, 190) Sum of transversal strengths at tire's 32 32 equatorialplane Transversal strength/circumferential 0.85 0.56 strength Breakingenergy 142 132 Presence of preceding break of carcass None None Trans.reinf. layer width/tread width 0.68 0.68 Presence of break at ends oftrans. None None reinf. layer during drum testing Straight cordconstituting trans. reinf. Non-expansible steel cord Non-expansiblesteel cord layer

TABLE 3 435/45R22.5 Comparative Example 3 Example 9 Structure Cir.reinf. layer 1(0, 300) Trans. reinf. layer (90, 260) (Inclined angle ofeach cord, width Cir. reinf. layer 2(0, 300) Cir. reinf. layer 1(0, 300)of each layer) Belt layer 1(L52, 370) Cir. reinf. layer 2(0, 300) Beltlayer 1(L52, 370) Sum of transversal strengths at tire's 16.3 34equatorial plane Transversal strength/circumferential 0.46 0.9 strengthBreaking energy 94 142 Presence of preceding break of carcass Yes NoneTrans. reinf. layer width/tread width — 0.68 Presence of break at endsof trans. — None reinf. layer during drum testing Straight cordconstituting trans. reinf. Non-expansible steel cord Non-expansiblesteel cord layer Comparative Example 4 Example 10 Structure Cir. reinf.layer 1(0, 300) Trans. reinf. layer (90, 260) (Inclined angle of eachcord, width Cir. reinf. layer 2(0, 300) Cir. reinf. layer 1(0, 300) ofeach layer) Belt layer 1(R52, 370) Cir. reinf. layer 2(0, 300) Beltlayer 2(L52, 210) Belt layer 1(R52, 370) Belt layer 2(L52, 210) Sum oftransversal strengths at tire's 16.3 34 equatorial plane Transversalstrength/circumferential 0.53 0.9 strength Breaking energy 102 147Presence of preceding break of carcass Yes None Trans. reinf. layerwidth/tread width — 0.68 Presence of break at ends of trans. — Nonereinf. layer during drum testing Straight cord constituting trans.reinf. Non-expansible steel cord Non-expansible steel cord layerComparative Example 5 Example 11 Structure S.belt layer(R60, 130–190)Trans. reinf. layer (90, 260) (Inclined angle of each cord, width Cir.reinf. layer 1(0, 330) S.belt layer(R60, 130–190) of each layer) Cir.reinf. layer 2(0, 330) Cir. reinf. layer 1(0, 330) Belt layer 1(R52,210) Cir. reinf. layer 2(0, 330) Belt layer 2(L52, 190) Belt layer1(R52, 210) Belt layer 2(L52, 190) Sum of transversal strengths attire's 17.7 34 equatorial plane Transversal strength/circumferential0.53 0.9 strength Breaking energy 101 150 Presence of preceding break ofcarcass Yes None Trans. reinf. layer width/tread width — 0.68 Presenceof break at ends of trans. — None reinf. layer during drum testingStraight cord constituting trans. reinf. Non-expansible steel cordNon-expansible steel cord layer

TABLE 4 285/60R22.5 Comparative Example 6 Example 12 Structure Cir.reinf. layer 1(0, 160) Trans. reinf. layer (90, 120) (Inclined angle ofeach cord, width Cir. reinf. layer 2(0, 160) Cir. reinf. layer 1(0, 160)of each layer) Belt layer 1(R20, 240) Cir. reinf. layer 2(0, 160) Beltlayer 2(L20, 220) Belt layer 1(R20, 240) Belt layer 3(L20, 120) Beltlayer 2(L20, 220) Belt layer 3(L20, 120) Sum of transversal strengths attire's 17.7 40.1 equatorial plane Transversal strength/circumferential0.25 0.63 strength Breaking energy 100 135 Presence of preceding breakof carcass Yes None Trans. reinf. layer width/tread width — 0.5 Presenceof break at ends of trans. — None reinf. layer during drum testingStraight cord constituting trans. reinf. Non-expansible steel cordNon-expansible steel cord layer Example 13 Comparative Example 7Structure Trans. reinf. layer (90, 180) Belt layer 1(R20, 240) (Inclinedangle of each cord, width Cir. reinf. layer 1(0, 160) Belt layer 2(L20,220) of each layer) Cir. reinf. layer 2(0, 160) Cir. reinf. layer 1(0,170) Belt layer 1(R20, 240) Cir. reinf. layer 2(0, 170) Belt layer2(L20, 220) Belt layer 3(L20, 170) Belt layer 3(L20, 120)) Sum oftransversal strengths at tire's 40.1 17.7 equatorial plane Transversalstrength/circumferential 0.63 0.25 strength Breaking energy 139 100Presence of preceding break of carcass None Yes Trans. reinf. layerwidth/tread width 0.75 — Presence of break at ends of trans. None —reinf. layer during drum testing Straight cord constituting trans.reinf. Non-expansible steel cord Non-expansible steel cord layer Example14 Structure Trans. reinf. layer(90, 180) (Inclined angle of each cord,width Belt layer 1(R20, 240) of each layer) Belt layer 2(L20, 220) Cir.reinf. layer 1(0, 170) Cir. reinf. layer 2(0, 170) Belt layer 3(L20,170) Sum of transversal strengths at tire's 40.1 equatorial planeTransversal strength/circumferential 0.63 strength Breaking energy 136Presence of preceding break of carcass None Trans. reinf. layerwidth/tread width 0.75 Presence of break at ends of trans. None reinf.layer during drum testing Straight cord constituting trans. reinf.Non-expansible steel cord layer

TABLE 5 285/60R22.5 Example 15 Example 16 Structure Trans. reinf. layer(90, 180) Trans reinf. layer (90, 180) (Inclined angle of each cord,width Belt layer 1(R20, 240) Belt layer 1(R20, 240) of each layer) Beltlayer 2(L20, 220) Belt layer 2(L20, 220) Cir. reinf. layer 1(0, 170)Cir. reinf. layer 1(0, 170) Cir. reinf. layer 2(0, 170) Cir. reinf.layer 2(0, 170) Belt layer 3(L20, 170) Belt layer 3(L20, 170) Sum oftransversal strengths at tire's 40.1 40.1 equatorial plane Transversalstrength/circumferential 0.63 0.63 strength Breaking energy 140 142Presence of preceding break of carcass None None Trans. reinf. layerwidth/tread width 0.75 0.75 Presence of break at ends of trans. NoneNone reinf. layer during drum testing Straight cord constituting trans.reinf. Expansible organic Expansible steel cord layer fiber cord(initial elongation 0.7%) (initial elongation 0.7%)

In Table 1, comparing Example 1 with Comparative example 1, it showsthat, as Example 1 is provided with a transversal reinforcement layer,the carcass is prevented from breaking before the other reinforcementlayers break, the breaking energy is enhanced and the durability againstthe repeated projection input is improved.

Comparing Example 1 with Example 2, it shows that the breaking energycan be increased by setting the sum of the transversal strength to 30kN/25 mm or more at the tire's equatorial plane.

In Tables 1 and 2, comparing Example 2 with Example 3, it shows that thebreaking energy is further effectively increased by setting the ratio ofthe transversal strength to the circumferential strength to 0.55 ormore.

In Table 2, comparing Example 3 with Example 4, it shows that thebreaking energy is further increased by widening the width of thetransversal reinforcement layer.

Comparing Example 4 with Example 5, the breaking energy is increased byraising the ratio of the transversal strength/the circumferentialstrength even for the tires having the same configuration.

Comparing Example 5 with Example 6, it shows that if the ratio of thewidth of the transversal reinforcement layer to the tread width is morethan 0.95, the durability of the tread rubber near the transversal endsof the transversal reinforcement layer, so that the ratio of the widthof the transversal reinforcement layer to the tread width is preferably0.95 or less.

In Table 3, comparing Comparative example 3 with Example 9, it showsthat arranging the transversal reinforcement layer gives highertransversal strength and larger breaking energy as well as prevents thecarcass from precedingly breaking even for the tire having a structurein which there is only one belt layer.

Comparing Comparative example 4 and Example 10, it shows that arrangingthe transversal reinforcement layer gives higher transversal strengthand larger breaking energy as well as prevents the carcass fromprecedingly breaking even for the tire having a structure in which oneof the belt layers is a wide belt layer.

Comparing Comparative example 5 with Example 11, it shows that arrangingthe transversal reinforcement layer gives higher transversal strengthand larger breaking energy as well as prevents the carcass fromprecedingly breaking even for the tire adopting split belts.

In Table 4, comparing Comparative example 6 with Examples 12 and 13, itshows that arranging the transversal reinforcement layer gives highertransversal strength and larger breaking energy as well as prevents thecarcass from precedingly breaking even for the tire having three beltlayers.

Comparing Comparative example 7 with Example 14, it shows that arrangingthe transversal reinforcement layer gives higher transversal strengthand larger breaking energy as well as prevents the carcass fromprecedingly breaking even for the tire in which the transversalreinforcement layer arranged radially outwardly on a belt layer andanother belt layer is arranged radially outwardly on the transversalreinforcement layer.

In Tables 4 and 5, comparing Example 14 with Examples 15 and 16, thebreaking energy is further increased, as the straight cords areextensible.

INDUSTRIAL APPLICABILITY

As clearly shown in the above description, the present invention cansuppress an increase of the weight of the whole tire, does not involve adecrease of the durability at the carcass ends, and can prevent thetransversal stiffness from being smaller than the circumferentialstiffness even for a low-profile tire in which the circumferentialreinforcement layer is arranged to suppress the radial growth of thetread at the shoulder portion, since the transversal reinforcement layeris arranged radially outwardly on the crown portion of the carcass.Therefore, even when the tire receives a projection input caused bypassing over a stone during the running on the road, the carcass can beprevented form breaking before the belt or the circumferentialreinforcement layer break.

1. A pneumatic tire, comprising: a carcass containing at least one toroidal carcass ply, a tread rubber arranged radially outwardly on the crown portion of the carcass, and a belt consisting of at least one belt layer arranged between the tread rubber and the carcass, said belt layer containing cords extending in a direction inclined from the tire's circumferential direction, wherein at least one circumferential reinforcement layer containing meandering cords extending generally along the tire's circumferential direction in a wavy or zigzag shape is provided radially outwardly or inwardly on the belt or between the belt layers, and at least one transversal reinforcement layer containing straight cords extending generally perpendicular to the tire's circumferential direction is provided on the position radially outwardly adjacent to the crown portion of the carcass, wherein the ratio of the sum of the transversal strengths of the carcass, the transversal reinforcement layer, the circumferential layer and the belt including their coating rubbers to the sum of the circumferential strengths of them is 0.55 or more at the tire's equatorial plane.
 2. A pneumatic tire, comprising: a carcass containing at least one toroidal carcass ply, a tread rubber arranged radially outwardly on the crown portion of the carcass, and a belt consisting of at least one belt layer arranged between the tread rubber and the carcass, said belt layer containing cords extending in a direction inclined from the tire's circumferential direction, wherein at least one circumferential reinforcement layer containing meandering cords extending generally along the tire's circumferential direction in a wavy or zigzag shape is provided radially outwardly or inwardly on the belt or between multiple belt layers, and at least one transversal reinforcement layer containing straight cords extending perpendicular to the tire's circumferential direction is provided on the position radially outwardly adjacent to the crown portion of the carcass, wherein the ratio of the sum of the transversal strengths of the carcass, the transversal reinforcement layer, the circumferential layer and the belt including their coating rubbers to the sum of the circumferential strengths of them is 0.55 or more at the tire's equatorial plane.
 3. A pneumatic tire, comprising: a carcass containing at least one toroidal carcass ply, a tread rubber arranged radially outwardly on the crown portion of the carcass, and a belt consisting of at least one belt layer arranged between the tread rubber and the carcass, said belt layer containing cords extending in a direction inclined from the tire's circumferential direction, wherein at least one circumferential reinforcement layer containing meandering cords extending generally along the tire's circumferential direction in a wavy or zigzag shape is provided radially outwardly or inwardly on the belt or between multiple belt layers, and at least one transversal reinforcement layer containing straight cords extending generally perpendicular to the tire's circumferential direction is provided on the position radially outwardly adjacent to the crown portion of the carcass, wherein the sum of the transversal strengths of the carcass, the transversal reinforcement layer, the circumferential reinforcement layer and the belt including their coating rubbers is 30 kN/25 mm or more at the tire's equatorial plane, and wherein the ratio of the sum of the transversal strengths of the carcass, the transversal reinforcement layer, the circumferential layer and the belt including their coating rubbers to the sum of the circumferential strengths of them is 0.55 or more at the tire's equatorial plane.
 4. The pneumatic tire according to claim 3, wherein the inclined angle of the straight cords of the transversal reinforcement layer with respect to the tire's circumferential direction is within a range of 90±20 degrees.
 5. The pneumatic tire according to claim 3, wherein the belt consists of one belt layer, and the inclined angle of the cords of the belt layer with respect to the tire's circumferential direction is 10 to 60 degrees.
 6. The pneumatic tire according to claim 3, wherein the belt consists of two or more belt layers; the cords of the adjacent belt layers cross each other; the inclined angle of the cords of the belt layers with respect to the tire's circumferential direction is 10 to 60 degrees; and the cords of the radially adjacent belt layers extend in the mutually opposite directions with respect to the tire's circumferential direction.
 7. The pneumatic tire according to claim 3, wherein the width of the transversal reinforcement layer is 0.35 times or more as large as the tread width.
 8. The pneumatic tire according to claim 3, wherein the width of the transversal reinforcement layer is 0.95 times or less as large as the tread width.
 9. The pneumatic tire according to claim 3, wherein the straight cords constituting the transversal reinforcement layer are non-extensible cords.
 10. The pneumatic tire according to claim 3, wherein the straight cords constituting the transversal reinforcement layer are extensible cords having an initial elongation of 0.2% or more.
 11. The pneumatic tire according to claim 10, wherein the straight cords constituting the transversal reinforcement layer are extensible organic fiber cords.
 12. The pneumatic tire according to claim 10, wherein the straight cords constituting the transversal reinforcement layer are extensible steel cords. 